The Island is the summit of a submarine mountain. It rises steeply to a central plateau dominated by rainforest. The plateau reaches heights of up to 360 metres and consists mainly of limestone with layers of volcanic rock.
The Island's 80 kilometre coastline is an almost continuous sea cliff reaching heights of up to 20 metres. There are thirteen places where breaks in the cliff give way to shallow bays and small sand and coral beaches. The largest of these bays forms the Island's port at Flying Fish Cove. The Island is surrounded by a coral reef. There is virtually no coastal shelf and the sea plummets to a depth of about 5000 metres within 200 metres of the shore. The climate is tropical and temperatures range from 21 °C to 32 °C. Humidity is around 80–90 per cent and south-east trade winds provide pleasant weather for most of the year. However, during the wet season between November and April, it is common for some storm activity to occur producing a swell in seas around the Island. The average rainfall is approximately 2000 mm per annum.
Christmas Island has a resident population of approximately 2072 with an ethnic composition of approximately 60 per cent Chinese, 25 per cent Malay and 15 per cent European.
Christmas Island was named on Christmas Day 1643 by Captain William Mynors, the Master of a passing ship. The first landing was recorded by William Dampier in 1688. For the next two centuries little interest was shown in the Island due to its rugged coastline.
Following the discovery of phosphate deposits the Island was annexed by Britain in 1888.
The Island was occupied by Japanese forces from March 1942 until the end of the Second World War and in 1946 became a dependency of Singapore. By agreement with the United Kingdom sovereignty was transferred to the Commonwealth of Australia on 1 October 1958 under the Christmas Island Act 1958. This day is still celebrated as Territory Day.
The Island's close proximity to South-East Asia and the equator has resulted in a diverse range of flora and fauna. There are 411 recorded plant species on Christmas Island and approximately 18 of these are native.
The distribution of plants on the island is related to soil depth moisture retention as well as exposure to and distance from the sea. A dense rainforest has evolved in the deep soils of the plateau and on some terraces. The forests are dominated by several tree species. Ferns, orchids and vines flourish on the branches in the humid atmosphere beneath the canopy.
The land crabs and sea birds are the most noticeable animals on the island. To date, 20 terrestrial and intertidal crabs have been described. The diversity and abundance of land crabs is not matched by any other island. Huge robber crabs, known elsewhere as coconut crabs, are also found on Christmas Island and are capable of opening and devouring coconuts with their strong claws.
Red crabs are dotted around the forest floor all over Christmas Island. The annual red crab mass migration to the sea to spawn has been described by ecologists as one of the wonders of the natural world. This migration takes place each year after the start of the wet season synchronised with the cycle of the moon.
The Island is also a focal point for sea birds of various species. Eight species or subspecies of sea birds nest on the Island. The most numerous is the Red-footed Booby, which nests in colonies in trees on many parts of the shore terrace. The widespread Brown Booby nests on the ground near the edge of the sea cliff and inland cliffs. Abbott's Booby (listed as endangered) nests on tall emergent trees of the western, northern and southern plateau rainforest. The Christmas Island forest is the only known nesting habitat of the Abbott's Booby left in the world.
The endemic Christmas Island Frigatebird (listed as endangered) has three well-defined nesting areas. Greater Frigatebirds nest in semi-deciduous trees on the shore terrace with the greater concentrations being in the North, West and South Point areas.
The Common Noddy and two species of bosuns or tropic birds with their distinctive streamer tail feathers also nest on the Island. Of the ten native land birds and shorebirds seven are endemic species or subspecies. Some 76 vagrant or migrant bird species have been recorded on the Island from time to time.
In 1989 the Australian Government documented Christmas Island's heritage and a number of Commonwealth owned commercial and residential properties have been listed on the Commonwealth Heritage List.